The invention relates to marine drives, and more particularly to a shock absorbing drive sleeve mounting the propeller to the propeller shaft.
The invention arose during continuing development efforts relating to marine drive sleeves such as shown in U.S. Pat. Nos. 5,244,348, 5,322,416, 5,484,264, incorporated herein by reference.
A shock absorbing drive sleeve protects the propeller shaft and the marine drive, including the gear train, when the propeller strikes an object. It is desirable to provide a drive sleeve which is sufficiently soft, i.e. low spring rate, to permit the propeller shaft to continue to rotate through a limited angle after the propeller has been stopped by an object, yet sufficiently strong or stiff, i.e. high spring rate, to support enough torque to propel the boat, including under high load conditions. These are conflicting design goals which require a trade-off between a low spring rate for shock absorption versus a high spring rate for torque bearing capability. The inventions of the above incorporated patents address and solve the noted trade-off, and afford both shock absorption and high load capability.
The present invention addresses the difference in torque bearing capability of a marine drive between forward and reverse. The forward drive components of the marine drive gear train, such as drive gears and clutches, have higher strength and greater torque bearing capability than the reverse drive components. This is because high load conditions, i.e. high speed, requiring high torque to propel the boat are encountered in the forward direction, but not in the reverse direction. Because the reverse drive components of the marine drive have lower strength, there is a need to protect same at lower torque levels, and hence it is desirable to provide a softer spring rate for reverse, i.e. a differential spring rate between reverse and forward. The present invention addresses and solves this need, and provides asymmetric shock absorption, i.e. different shock absorption characteristics between forward and reverse. In preferred form, this is accomplished by simple modification to the drive sleeves of the above noted incorporated patents.